This invention relates to a reduction drive device for a power transmission system installed on an electric motor side of an electric vehicle employing an electric motor as a drive source or a four-wheel-drive hybrid electric vehicle employing an engine (internal combustion engine) and an electric motor as drive sources.
A conventional reduction drive device is, for example, the one shown in FIG. 6. In FIG. 6, the reduction drive device 201 reduces output of an electric motor 203 and transmits the same to left and right axle shafts to drive, for example, left and right rear wheels. The electric motor 203 is used as a supplementary drive source. A front-wheel side employs an engine such as an internal combustion engine as a main drive source to drive left and right front wheels.
The reduction drive device 201 has a casing 205 that supports a reduction mechanism 206 and a differential gear 207. The differential gear 207 is coupled with the axle shafts interlinked with, for example, the left and right rear wheels. The electric motor 203 is fastened and fixed to a motor joint 209 of the casing 205 with bolts 211.
The reduction mechanism 206 reduces rotational output of the electric motor 203 and the reduced rotational output is distributed through the differential gear 207 to the left and right axle shafts.
According to such a reduction drive device 201, the electric motor 203 extremely protrudes from the motor joint 209 of the casing 205 in an axial direction (rightward in FIG. 6), thereby enlarging the total size of the device, easily causing the electric motor 203 to vibrate, and limiting noise/vibration controllability.
Patent literature 1: Japanese Unexamined Patent Application Publication No. 2004-293584